The TRIM and EXTEND commands are a powerful pair of commands, and you will find many practical, real-world applications for these commands.
For example, you can use TRIM and EXTEND to modify the lines on the left to create the shaft shown on the right.
Start with the EXTEND command. On the Home ribbon, in the Modify panel, click the Extend tool. In the command line, the program displays the current settings. Note that Edge mode is currently set to None. The program displays the current modes when you first start the command, and it is important to take note of these settings. When Edge mode is set to none, you can only trim or extend objects that would actually intersect the boundary or cutting edges. In this example, you will need to change the Edge mode to Extend, but before you can do that, you must first select the objects that will be the boundary or cutting edges.
In this particular example, everything is going to be either a boundary edge or a cutting edge, except for the short horizontal line segments. Those are already in the proper location and will not be used to extend or trim other objects. So there is no need to include them. When you select cutting edges or boundary edges, you do not need to select everything. Just select those objects that actually need to be used as cutting or boundary edges. Use a crossing window to select the boundary edges and then right-click or press ENTER to complete that selection. The objects you selected as boundary edges are highlighted.
Now the program prompts you to select the objects to extend and also displays additional options. Now you can change the edge mode. Right-click and choose Edge and then choose Extend.
Now you can start choosing the objects you want to extend. Each time you move the cursor over an object, you can see a preview of how the object will be extended. The direction in which the object will be extended depends on where you select it. Each line will be extended in the direction closest to the end at which you pick the object. If you click the object again, it will extend to the next boundary edge.
Once you have extended all the lines that need to be extended, you are ready to start trimming. Even though you started with the EXTEND command, you can press and hold down the SHIFT key to immediately start trimming lines. And here is a tip: when extending objects, the best approach is usually to start from the inside and work your way out. When trimming lines, it usually works best to reverse the process: start from the outside and work your way back toward the inner-most portions of the object. Because if you were to start at the inside, you might accidently leave some smaller line segments out at the end. For example, when you move the cursor over the vertical line on the left, if you do not start from the end of the line, the command preview shows you that you would end up with a short segment left behind that you would then need to erase.
The command preview makes it very easy to see the results of your actions before you click. When trimming, the segment to be removed is dimly displayed, and a cursor badge indicates that it will be deleted.
Continue trimming objects, always working from the outside in. Remember, that you are pressing and holding the SHIFT key as you click to select objects. Once you have finished trimming objects, you can release the SHIFT key and then press ENTER or ESC to end the command.